Although magnetic "bubble" technology is relatively recent, the evolution of this technology has proceeded at a rapid pace. In this technology, various types of garnet compositions, prepared as magnetic epitaxial films (on a suitable non-magnetic substrate) and grown with growth or stress induced uniaxial anisotropy, are now available. Through known techniques, single wall cylindrical domains or "bubbles" (i.e. areas of one particular magnetic polarization) are established in a film which is otherwise saturated in the opposite magnetic polarization. Methods and techniques for generating such bubble domains in a magnetic film are known in the art.
This type of device (i.e. bubble domain detection device) has been proposed as a new electronic circuit device or component. At present, the major foreseeable utilization of magnetic bubble domain devices and materials is in the area of magnetic memory devices. As in any other memory device, the interest is in optimizing the number of bits per unit area and, thus, storage density. Clearly, the smaller the diameter of the individual bubble in the device, the more bubbles per unit area and, consequently, the greater the information storage density. However, as the bubble diameter decreases, bubble detection becomes increasingly difficult in view of the relatively strong magnetic effects of the demagnetizing fields in comparison to the fields generated by the bubble domains.
Several detector designs have been investigated to alleviate this detection problem. For example, detectors having the configuration of a large disk or a large rectangular shape have been tried. A relatively recent detector design has been suggested in a paper entitled "An Overview of Magnetic Bubble Domains-Material Device Interface" , Proceedings of the 17th Annual Conference on Magnetism and Magnetic Materials, Chicago, 1971, Part 1, pages 45-55 by A. H. Bobeck et al. This detector is known as the "Chinese character detector" and, effectively, stretches the bubble domain. However, this detector causes the bubble domain to be stretched in a direction parallel to or along the propagation direction of the bubble. While this design, which is essentially three detectors in series, results in an output signal which is approximately 2.5 times larger than signals produced by single detector elements, other problems are encountered. For example, the Chinese character detector requires increased bubble velocity in order to achieve propagation past the detector which may reduce the data rate for the overall bubble device. In addition, the operating margins and, hence, the reliability at a given data rate is reduced for the overall bubble device. Consequently, it has become apparent that a new and improved detection technique and device is required which permits the magnetic device to utilize small diameter bubbles, provide high reliability and to effect a data handling capability capability and a data rate which is commensurate with the associated propagation pattern and the overall device.